Inertial sensors are sensors configured to measure various types of movement, such as acceleration, tilt, shock, vibration, rotation, and multiple degrees-of-freedom (DoF) motion. Inertial sensing has found use in a wide variety of fields and applications and have been incorporated into many devices, including smartphones, tablets, gaming systems, automotive, and power tool. Inertial sensors are typically implemented by multiple sensor devices that are each configured to measure a movement related parameter along multiple axes, e.g., 3-axis accelerometers, 3-axis gyroscopes, and/or 3-axis magnetic field sensors. The output of these devices can be combined to quantify different types of movement.
One difficulty faced in inertial sensor technology is finding ways to package inertial sensors that enables multiple DoF systems (e.g,. 6DoF and 9DoF) to be realized in packaging sizes that can be incorporated into handheld or portable devices with small housing/enclosure or housing with limited space, such as smartphones, tablet, diagnostic tools, scan-tools, and portable corded/cordless power tools. For example, inertial sensors are typically implemented as MEMS sensors utilizing capacitive detection techniques. Capacitive MEMS sensors, however, are generally not capable of being efficiently integrated into complementary metal-oxide semiconductor (CMOS) processing and have a rather large footprint, e.g., 2.5×2.5 mm2. Packaging methods, such as chip-stacking and hybrid integration, are commonly used to package capacitive MEMS sensors which result in package sizes that are approximately 3×3 mm2 or larger.
Footprint sizes of less than 2.5×2.5 mm2, e.g. 1×1 mm2 . . . 2×2 mm2, with a height of less than 1 mm (target: below 0.5 mm) are typically required for incorporation into mass-market handheld or portable devices. However, these two requirements can hardly be met with conventional technology. For example, the current smallest package sizes of 6DoF inertial sensor systems (e.g., 3-axis accelerometer and 3-axis gyroscope) is 4×4 mm2 footprint with 0.9 mm height. A footprint of 2×2 mm2 for 6DoF systems is not feasible with current technological approaches. Stacking of single chips allows theoretically a small footprint of 2.5×2.5 mm2, however, this is only possible by increasing the height of the sensor footprint above 1 mm.